Lithium metal oxide materials and methods of synthesis and use

ABSTRACT

A composition having a formula Li x Mg y NiO 2  wherein 0.9&lt;x&lt;1.3, 0.01&lt;y&lt;0.1, and 0.91&lt;x+y&lt;1.3 can be utilized as cathode materials in electrochemical cells. A composition having a core, having a formula Li x Mg y NiO 2  wherein 0.9&lt;x&lt;1.3, 0.01&lt;y&lt;0.1, and 0.9&lt;x+y&lt;1.3, and a coating on the core, having a formula Li a Co b O 2  wherein 0.7&lt;a&lt;1.3, and 0.9&lt;b&lt;1.2, can also be utilized as cathode materials in electrochemical cells.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the benefitof priority under 35 U.S.C. § 120 of copending U.S. patent applicationSer. No. 10/850,877, entitled LITHIUM METAL OXIDE MATERIALS AND METHODSOF SYNTHESIS AND USE, filed on May 21, 2004, issued as U.S. Pat. No.7,381,496, which is incorporated herein by reference in its entirety forall purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lithium metal oxide compositions aswell as electrochemical devices utilizing such compositions and, inparticular, to lithium-magnesium nickel oxide compositions suitable ascomponents of lithium-ion electrochemical devices.

2. Description of Related Art

Rechargeable lithium and lithium-ion batteries can be used in a varietyof applications, such as cellular phones, laptop computers, digitalcameras and video cameras, and hybrid electric vehicles etc., due totheir high energy density.

Commercially available lithium-ion batteries typically consist ofgraphite-based anode and LiCoO₂-based cathode materials. However,LiCoO₂-based cathode materials can be expensive and typically haverelatively low capacity, approximately 150 mAh/g.

Alternatives to LiCoO₂-based cathode materials include LiNiO₂-basedcathode materials, which can be less expensive. Typical LiNiO₂-basedcathode materials can include compositions having a formulaLiNi_(0.8)Co_(0.2)O₂ or LiNi_(0.8)Co_(0.15)Al_(0.05)O₂. These materialsare relatively more expensive than cobalt-free LiNiO₂-based cathodematerial because of the relatively higher cost of cobalt relative tonickel. Furthermore, LiNiCoO₂-based cathode materials usually have lowersafety, cyclability, and first cycle efficiency over LiCoO₂-basedcathode materials because of the lower structural stability and highersurface reactivity of LiNiO₂ type cathodes.

Li(Ni, Co)O₂-based cathode materials have also been disclosed. Forexample, Lecerf et al., in U.S. Pat. No. 4,980,080, disclosed a processof making a cathode material for a secondary battery having a formulaLi_(y)Ni_(2-y)O₂ or Li_(1-x)Co_(x)O₂. Xie et al., in U.S. Pat. No.5,750,288, disclosed modified lithium nickel oxide compounds forelectrochemical cathodes and cells based on Li_(x)M_(y)O_(z) materials,where M is a non-transition metal selected from the group consisting ofaluminum, gallium, tin and zinc. Mayer, in U.S. Pat. No. 5,783,333,disclosed a Li_(x)Ni_(y)Co_(z)M_(n)O₂ material. Mayer also disclosed, inU.S. Pat. Nos. 6,007,947 and 6,379,842, cathode materials having aformula Li_(x)Ni_(y)Co_(z)M_(n)O₂ or Li_(x)Mn_(2-r)M1_(r)O4 where M is ametal selected from the group consisting of aluminum, titanium,tungsten, chromium, molybdenum, magnesium, tantalum, silicon, andcombinations thereof and M1 is one of chromium, titanium, tungsten,nickel, cobalt, iron, tin, zinc, zirconium, silicon, or a combinationthereof. Kumta et al., in U.S. Pat. No. 6,017,654, disclosed cathodematerials having a formula Li_(1+x)Ni_(1-y)M_(y)N_(x)O_(2(1+x)) andLiNi_(1-y)M_(y)N_(x)Op where M is a transition metal selected from thegroup consisting of titanium, vanadium, chromium, manganese, iron,cobalt, and aluminum and N is a Group II element selected from the groupconsisting of magnesium, calcium, strontium, barium, and zinc. Sunagawaet al., in U.S. Pat. No. 6,040,090, disclosed a positive electrodematerial based on Li—Ni—Co—Mn—O₂. Peres et al., in U.S. Pat. No.6,274,272, disclosed an active cathode material having a formulaLi_(L)Ni_((1-C-A-M))Co_(C)A1_(A)Mg_(M)O₂. Gao et al., in U.S. Pat. No.6,277,521, disclosed a lithium metal oxide material containing multipledopants with a formula LiNi_(1-x)Co_(y)M_(a)M′_(b)O₂ where M is a metalselected from the group consisting of titanium, zirconium, andcombinations thereof and M′ is a metal selected from the groupconsisting of magnesium, calcium, strontium, barium, and combinationsthereof. Mao et al., in U.S. Pat. No. 6,071,649, disclosed LiCoO₂-coatedLiNiO₂ or Li(Ni, Co)O₂ materials. None of these disclosedLi—Mg—Ni—O₂-based cathode materials.

Matsubara et al, in U.S. Pat. No. 6,045,771, disclosed a cathodematerial having a formula Li_(y-x1)Ni_(1-x2)M_(x)O₂, where M is a metalselected from the group consisting of aluminum, iron, cobalt, manganese,and magnesium, x=x1+x2, 0<x1≦0.2, 0<x2≦0.5, 0<x≦0.5, and 0.9<y≦1.3.

Multiple companies are also commercially fabricating cathodes utilizingmaterials with a general formula LiNiCoMO₂. TODA (earlier Fuji Chemical)manufactures products CA5, CA1505N, and NCA. Honjo-FMC and Nichia (bothof Japan) also provide nickel-cobalt-based cathodes. These productstypically suffer from low safety properties, and relatively low ratecapability.

BRIEF SUMMARY OF THE INVENTION

In accordance with one or more embodiments, the t present inventionrelates to Li_(x)Mg_(y)NiO₂ materials, which, when utilized inelectrochemical applications or systems, can be characterized as beingor providing systems that utilize safer, low-cost cathode materials withhigh capacity, long cycle life, high rate, especially high powerability,as well as high voltage. In some embodiments, the cathode materials ofthe present invention can be characterized as being lower cost, havingimproved chemically stability, and higher operating voltage whileproviding greater capacity especially, for example, relative to LiCoO₂—and/or LiNiO₂— based cathode materials.

In accordance with one or more embodiments, the present inventionprovides a composition having a formula Li_(x)Mg_(y)NiO₂ wherein0.9<x<1.3, 0.01<y<0.1, and 0.91<x+y<1.3.

In accordance with further embodiments, the present invention provides acomposition comprising a core having a formula Li_(x)Mg_(y)NiO₂, wherein0.9<x<1.3, 0.01<y<0.1, and 0.91<x+y<1.3, and a coating on the corehaving a formula Li_(a)Co_(b)O₂, wherein 0.7<a<1.3, and 0.9<b<1.2.

In accordance with one or more embodiments, the present inventionprovides an electrochemical cell comprising a cathode comprising acomposition having a formula Li_(x)Mg_(y)NiO₂, wherein 0.9<x<1.3,0.01<y<0.1, and 0.91<x+y<1.3.

In accordance with one or more embodiments, the present inventionprovides an electrochemical cell comprising a cathode comprisingparticles consisting of a core having a formula Li_(x)Mg_(y)NiO₂,wherein 0.9<x<1.3, 0.01<y<0.1, and 0.91<x+y<1.3, and a coating on thecore. The coating can have a formula Li_(a)Co_(b)O₂, wherein 0.7<a<1.3,and 0.9<b<1.2.

A method of preparing a composition comprising providing a mixture ofcompounds comprising a lithium source, a magnesium source, and a nickelsource and reacting the mixture in an oxidizing atmosphere at atemperature and for a period sufficient to crystallize the mixture intoa Li_(x)Mg_(y)NiO₂ composition wherein 0.9<x<1.3, 0.01<y<0.1, and0.91<x+y<1.3.

In accordance with one or more embodiments, the present inventionprovides a method of preparing coated particles. The method can comprisesteps of providing a first mixture of compounds comprising lithium,magnesium, and nickel and sintering the first mixture in an oxidizingatmosphere at a first temperature and for a first period sufficient tocrystallize the first mixture into core particles having a formulaLi_(x)Mg_(y)NiO₂, wherein 0.9<x<1.3, 0.01<y<0.1, and 0.91<x+y<1.3; andcoating the core particles with a second mixture comprising compoundscomprising lithium and cobalt and sintering the coated core particles ata second temperature and for a second period sufficient to crystallizethe coating having a formula Li_(a)Co_(b)O₂ wherein 0.7<a<1.3, and0.9<b<1.2.

In accordance with one or more embodiments, the present inventionprovides a particle comprising a core material having a composition of aformula Li_(1-y)Mg_(y)NiO₂ where Mg and Li are predominantly in acrystallographic 3a site and Ni is predominantly in a crystallographic3b site and 0.01<y<0.1.

Other advantages, novel features, and objects of the invention shouldbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings, which areschematic and not intended to be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred, non-limiting embodiments of the present invention will bedescribed by way of example with reference to the following,accompanying drawings. In the drawings, each identical or nearlyidentical component that is illustrated in various figures is typicallyrepresented by a like numeral. For clarity, not every component may belabeled in every drawing nor is every component shown where illustrationis not necessary to allow those of ordinary skill in the art tounderstand the invention. In the drawings:

FIG. 1 is a copy of photomicrograph, representing a typicallithium-magnesium-nickel oxide composition in accordance with one ormore embodiments of the present invention; here represented by sphericalLiMg_(0.025)NiO₂;

FIG. 2 is an X-ray diffraction pattern of the composition shown in FIG.1;

FIG. 3 is a graph showing the discharge profile, at different dischargerates, of the material shown in FIG. 1;

FIG. 4 is a copy of photomicrograph of a typical lithium-cobaltoxide-gradient coated lithium-magnesium-nickel oxide composition inaccordance with one or more embodiments of the present invention; hererepresented by an about 5 mol % LiCoO₂:LiMg_(0.025)NiO₂;

FIG. 5 is an XRD graph of the coated composition shown in FIG. 4;

FIG. 6 is a graph showing the discharge profile of the composition shownin FIG. 4 having about a 5 mol % coating level at various rates;

FIG. 7 is a graph showing the discharge profile of the composition shownin FIG. 4 having about a 10 mol % coating level at various rates;

FIG. 8 is a graph showing the discharge profile of the composition shownin FIG. 4 having about a 15 mol % coating level at various rates;

FIG. 9 is a graph showing the area specific impedance for aLiMg_(0.025)NiO₂ composition with about a 5 mol % LiCoO₂ gradientcoating, using about a 1 s and an 18 s pulse according to protocol 3, inaccordance with one or more embodiments of the invention;

FIG. 10 is a graph showing the area specific impedance for variousLiMg_(0.025)NiO₂ compositions, using 1 s and 18 s pulses according toprotocol 3, in accordance with one or more embodiments of the invention;

FIG. 11 is a graph showing the X-ray diffraction patterns showing peakprofiles at about 5 mol %, 10 mol %, and 15 mol % gradient coatinglevels of a LiCoO₂ composition (with an enlarged portion shown in theright side), in accordance with one or more embodiments of theinvention;

FIG. 12 is a graph showing the capacity retention of cells during abouta 1 C discharge cycling utilizing a) LiNiO₂, b) LiMgNiO₂, c) about 5 mol% LiCoO₂ coated LiMg_(0.025)NiO₂, and d) CA1505N (TODA Co., Japan); and

FIG. 13 is a graph showing the differential scanning calorimetry profileof a) LiMg_(0.025)NiO₂, b) about 5 mol % LiCoO₂ coated LiMg_(0.025)NiO₂,and c) TODA NCA-02 electrodes, which have been subjected to about 4.2Vcharging (100% state-of-charge) and immersed in electrolyte.

DETAILED DESCRIPTION OF THE INVENTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components or compounds set forth inthe following description, including the various examples, orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced or of being carried out in variousways. Also, the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting. The useof “including,” “comprising,” or “having,” “containing,” “involving,”and variations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

In accordance with one or more embodiments, the present inventionprovides one or more compositions and one or more methods for formingthe various compositions. The compositions can be used as a cathodeactive material in, for example, rechargeable lithium and lithium-ionelectrochemical devices, such as but not limited to, batteries. Inaccordance with one or more embodiments, the present invention can alsoprovide rechargeable lithium batteries or lithium-ion batteries, as wellas methods of preparation and use, utilizing, for example, thecompositions of the invention. The electrochemical cells utilizing thecompositions of the present invention can be characterized as, interalia, being low cost and chemically stable while providing high capacityduring a long operating life.

In accordance with some embodiments, the composition of the presentinvention typically exhibits improved capacity, cyclability, and safetyover LiCoO₂ and LiNiO₂ materials when such materials are utilized inelectrochemical devices, including, but not limited to primary andsecondary batteries. The materials of the present invention can provideeconomic advantages because they are typically less expensive to produceand/or utilize compared to LiCoO₂, LiNiO₂ or LiNi_(0.8)Co_(0.2)O₂-basedmaterials.

In accordance with one or more embodiments, the present inventionprovides a lithium metal oxide composition having a first metalsubstantially associated with an a-site and a second metal substantiallyassociated with a b-site in a crystalline lattice. The a-site can becrystallographically referred to as the 3a site and the b-site can bereferred to as the 3b site in a R3m crystal lattice. In accordance withsome embodiments of the invention, the first metal can be associated atthe 3a site along with, for example, lithium, and the second metal canbe associated at the 3b site. Preferably, the first metal or, in somecases the second metal, can provide crystalline stability during lithiumintercalation and de-intercalation processes when, for example, thematerials or compositions of the present invention are utilized ascomponents of electrochemical devices. By providing such a structure,the composition of the present invention can be advantageously utilizedas a cathode in electrochemical devices because, it is believed, thefirst metal can stabilize, at least partially, the crystal latticeduring lithium intercalation and de-intercalation processes.

In accordance with one or more preferred embodiments of the invention,the composition can comprise a lithium-magnesium-nickel oxide whereinlithium and magnesium are crystallographically associated with the 3asite and nickel is crystallographically associated with the 3b site.

In accordance with one or more embodiments, the present inventionprovides a composition having a general formula Li_(x)Mg_(y)NiO₂, where0.9<x<1.3, and 0.01<y<0.1, 0.91<x+y<1.3, preferably, 0.9<x<1.1 and0.02<y<0.05. The crystalline characteristics of the composition can becharacterized as having lithium and magnesium associated with the 3asite and the nickel as being associated with the 3b site.

In accordance with further embodiments, the present invention provides aparticle comprising a core or interior layer having one or more layersof a metal oxide coating applied thereon. The coating layer can comprisea second lithium intercalating material including, for example, acompound having a formula Li_(a)Co_(b)O₂, where 0.7<a<1.3, and0.9<b<1.2. In some cases, the coating layer can be characterized ashaving a Co/Ni molar ratio that ranges from about 0.01 to about 1.4,relative to the amount of nickel in the core layer. In still furtherembodiments of the invention, 0.9<a<1.3, 1.8<b<2.2 and the Co/Ni molarratio can range from about 0.02 to about 0.8. The one or more layers canbe characterized as having a concentration gradient with respect to theamount of cobalt relative to distance, e.g. radial distance, from thesurface of the particle. The nature of the concentration gradient of theamount cobalt, relative to distance from the surface, can range fromabout 100%, substantially all cobalt and none or only negligible traceamounts of nickel, at the outer surface of the particle to about 0%,substantially none or only negligible trace amounts of cobalt at thecoating/core interface. The nature or shape of the gradient profile canvary. For example, the gradient profile can linearly decrease relativeto radial distance from the surface.

In accordance with still further embodiments, the invention can becharacterized as providing a particle comprising a lithium magnesiumnickel oxide core having a lithium cobalt oxide coating layer. Theamount of the coating layer can range from about 0.01 wt % to about 30wt % of the particle.

The present invention further provides one or more synthesis techniquesthat provides a first metal having a preferential association with the3a site and, in some cases, provides a second metal having apreferential association with the 3b site. In accordance with stillother embodiments, the present invention provides synthesis techniquesthat can decrease any tendency by the second metal to associate with the3a site.

The first metal can provide crystalline stability to the lithium mixedmetal oxide material during lithium intercalation/de-intercalationcycling processes. Thus, the techniques of the present invention canprovide a chemically stable material that may be suitable as components,e.g. cathodes, in electrochemical devices and be characterized as havinghigh capacity, low cost as well as high voltage and high rate withimproved cycle life.

In accordance with one or more embodiments, the techniques of thepresent invention can utilize precursor compounds that can form alithium metal oxide, preferably a lithium metal oxide doped with acrystal lattice stabilizing metal. In accordance with other embodiments,the techniques of the present invention can provide or promoteprocessing conditions that favor the formation of ionic species fromprecursor compounds that can preferentially become associated withspecific crystallographic sites. The processing conditions of thepresent invention can promote formation of metal oxide species as wellas association of such species with a particular, predeterminedcrystallographic site. For example, the techniques of the presentinvention can utilize one or more lithium donor compounds, one or moremetal donor compounds that preferentially can become associated with a3a crystallographic site, and in some cases, one or more metal donorcompounds that preferentially become associated with a 3bcrystallographic site. Thus, in accordance with one or more embodiments,the present invention can utilize a lithium donor compound, a magnesiummetal donor compound, and a nickel metal donor compound; the processingconditions can promote ionic species formation, intermingling, andcrystallization to form a lithium mixed metal oxide wherein a firstmetal can be preferentially associated with a 3a crystallographic siteand a second metal can be preferentially associated with a 3b site.

In accordance with further embodiments, the techniques of the presentinvention can provide a lithium magnesium nickel oxide composition. Forexample, one or more techniques can utilize precursor compoundsincluding, for example, those selected from the group consisting of alithium donor, a magnesium donor, and a nickel donor. In some cases, oneor more oxidizing agents or compounds can also be utilized. Thus, theprecursor compound mixture can comprise, for example, a lithium source,an oxidizing agent, a first metal donor, and a second metal donor. Thelithium source, the oxidizing agent, the first metal donor, and thesecond metal donor, preferably, can undertake one or more phase changesor phase transitions at about the same processing conditions, e.g., atabout the same processing temperature range. Preferably, the elements ofthe selected precursor compounds can maintain their respectivepredetermined valences until, or in some cases through, the phasechange. Likewise, the processing conditions utilized inhibit or at leastdo not promote any valence changes. Thus, in accordance with one or morepreferred embodiments of the present invention, the precursor compounds,or oxides of the respective donor components, can be subject toprocessing conditions that promote or maintain chemical stability untilreaction to a desired phase.

The lithium donor or source can comprise lithium hydroxide, lithiumcarbonate, or mixtures thereof. The oxidizing agent can comprise lithiumnitrate or nickel nitrate or mixtures thereof. In some cases, thelithium source can comprise or consist of lithium nitrate as well aslithium hydroxide. The first metal donor can comprise magnesiumhydroxide, magnesium carbonate, magnesium oxide, or mixtures thereof.The second metal donor can comprise nickel hydroxide, nickel sulfate,nickel nitrate, nickel oxide, or mixtures thereof.

The precursor compounds can have any form that facilitates mixing intothe precursor mixture. For example, the precursor mixture can comprise apowder mixture of each of the precursor compounds or a slurry of each ofthe precursor compounds. Moreover, the precursor compound can be amasterbatch comprising hydroxides of lithium, the first metal donor,and/or the second metal donor. The oxidizing agent can be incorporatedinto the masterbatch as desired to facilitate processing and storagebefore utilization. In accordance with one or more embodiments, theprecursor compounds can have any desired structure that, preferably,promotes efficient utilization of the lithium metal oxide materials ofthe present invention. Thus, the synthesis techniques of the inventioncan provide morphologically desirable lithium metal oxide materials.

The precursor compounds can have a variety of shapes that can betransformed to a material that can coat or be coated to form a componentof an electrochemical device. For example, one or more of the precursorpowder compounds can be spherically-shaped. Other shapes can be utilizedas desired to accommodate or suit an end-user preference. Preferably,the synthesis process of the present invention can maintain, at leastpartially, the spherical shape throughout the processing or synthesissteps to provide, for example, a lithium magnesium nickel oxide materialsuitable as a cathode electrode in, for example, rechargeableelectrochemical devices. Thus, in accordance with one or more preferredembodiments, the precursor mixture comprises a nickel donor, such as butnot limited to nickel hydroxide, having a spherical shape. However, anyshape and form of the starting materials of the composition of thepresent invention can be utilized.

In accordance with still further embodiments, the nickel donor cancomprise a high density, e.g., high tap density, nickel hydroxide.

The Li_(x)Mg_(y)NiO₂ compositions of the present invention can beprepared by utilizing precursor compounds with pre-defined orpre-selected particle sizes and morphologies. Any particle size can beutilized to create the composition of the present invention. Forexample, the particle size of a nickel donor precursor such as Ni(OH)₂can be in the range of about 2 μm to about 20 μm.

In accordance with one or more embodiments, the material molar ratios ofthe precursor compounds can be selected to provide a composition havingthe general material formula Li_(x)Mg_(y)NiO₂, where 0.1<x<1.3, and0.01<y<0.1, 0.9<x+y<1.3. In some cases, the ratios can be selected to sothat 0.9<x<1.1, and 0.02<y<0.05. In still other cases, x can be about1−y.

In yet other embodiments in accordance with the present invention, theLi_(x)Mg_(y)NiO₂ or Li_(1-y)Mg_(y)NiO₂ materials can have any one of thefollowing formula: Li_(1.05)Mg_(0.005)NiO₂, Li_(1.05)Mg_(0.01)NiO₂,Li_(1.05)Mg_(0.02)NiO₂, Li_(1.05)Mg_(0.025)NiO₂,Li_(1.05)Mg_(0.030)NiO₂, Li_(1.05)Mg_(0.04)NiO₂, andLi_(1.05)Mg_(0.05)NiO₂. Thus, the precursor compounds can be selected insuch ratios that provide such compositions.

The precursor compounds are typically pre-mixed to allow homogeneousmixing. In still further embodiments, the materials of the presentinvention can be crystallized by, for example, heating to sinter andfacilitate crystallization into the compositions of the presentinvention.

The synthesis process can comprise mixing the precursor compounds into asubstantially homogeneous mixture. The synthesis process can furthercomprise heating the precursor mixture in one or more heating stages orsteps, e.g., two or more heat soaks, according to a predeterminedheating profile. The synthesis process typically promotes oxidation, oroxyhydroxide formation, of the corresponding donor components; mixing,typically ionic mixing, of such components; and crystallization into alithium metal oxide composition, wherein the first metal of thecomposition, e.g., magnesium, is associated with a 3a site and thesecond metal, e.g., nickel, is associated with the 3b site. For example,in a lithium-magnesium-nickel oxide composition, the mixture can beheated to a first heating temperature that promotes preferentialformation of Ni³⁺ over Ni²⁺.

In accordance with one or more embodiments of the invention, the firstheating step or stage can involve heating the green, precursor mixtureto allow oxide formation and/or ion mixing without, or at least minimal,valence changes of the donor compounds. For example, the precursormixture can be heated to a heat soak temperature of about 450° C. in afirst heating step. This first heat soaking temperature can range fromabout 350° C. to about 700° C. The second heating step can compriseheating to promote crystallization of the transformed oxide mixture by,for example, heat soaking at a second heat soak temperature of about700° C. The second heat soaking temperature can range from about 600° C.to about 800° C.

Preferably, the first soaking temperature is maintained until theprecursor compounds have been substantially transformed into their oxidecounterparts. For example, the first soaking temperature can bemaintained for about one hour but can be maintained for as long as aboutsix hours. In accordance with other embodiments, the first heat soakcondition can be maintained for any duration such that the synthesisprocedure can proceed to the next heating stage to commence or promotecrystallization, i.e., without maintaining a first soaking temperature.The second soaking temperature can be maintained, for example, until thelithium metal oxide has crystallized to a desired extent. Thus, forexample, the second heat soak can be maintained for about one hour butcan be maintained for as long as about six hours.

Heating, as well heat soaking, can be performed with exposure to anoxidizing atmosphere such as air or pure oxygen.

The first heating step can comprise raising the temperature at a ratesufficient to promote oxide formation while reducing any tendency todestabilize the precursor morphology. For example, the precursor mixturecan be heated at a rate of about 20° C. per minute, about 10° C. perminute, or even about 5° C. per minute. Control of the heating rate maydepend on several factors including, but not limited to, the amountbeing processed, the desired relative composition, as well as theeffective area exposed to the oxidizing atmosphere. The second heatingstage can comprise raising the temperature to be sufficient tofacilitate crystallization such that the first metal tends to beassociated with the 3a site and the second metal tends to be associatedwith the 3b site. For example, the oxide mixture can be heated at a rateof about 10° C. per minute, about 5° C. per minute, or even about 2° C.per minute.

After heat treatment, the materials can be allowed to cool naturally toroom temperature by, for example, natural convection. Heat soaking canbe performed in any suitable equipment. For example, a furnace or ovenaccommodating the mixture can be utilized. The furnace can be suppliedwith air and/or oxygen.

The sintered, crystallized material can be ground in any suitablegrinding apparatus. For example, a mortar grinder (e.g., Model RM100grinder available from Retsch/Brinkmann or Brinkmann Instruments, Inc.,Westbury, N.Y.) fitted with an agate mortar and pestle, can be utilizedto grind the crystallized composition to render it with a desiredparticle size. Other suitable grinding methods or systems can include,for example, ball milling, jet milling, attritor mill, hammer mill andpin mill-devices. The desired particle size can vary and can depend onthe specific application or use. Thus, in accordance with one or moreembodiments of the invention, the Li_(x)Mg_(y)NiO₂ composition can beformed as particles by grinding for about five minutes until a meanparticle size of about 2 μm to about 20 μm, preferably about 5 μm toabout 10 μm, is achieved.

In accordance with one or more preferred embodiments of the presentinvention, the Li_(x)Mg_(y)NiO₂ composition, typically as particles, canfurther comprise a coating layer that further improves a first cycleefficiency, life, and/or safety or even reduces gassing when thecomposition is utilized as a cathodic material in electrochemicaldevices. In accordance with still further embodiments of the invention,the Li_(x)Mg_(y)NiO₂ particles further comprise one or more coatinglayers that reduces any gelling tendencies when the particles areprepared as an electrode paste. For example, the particles can be coatedto reduce the likelihood of gelling in a mixture comprising NMP, PVDF,Li_(x)Mg_(y)NiO₂, and conductive carbon, which is yet another advantageover non-coated nickelates.

In accordance with one or more embodiments of the invention, the coatinglayer can comprise a composition having a formula LiCoO₂. The coatedLi_(x)Mg_(y)NiO₂ particles can be prepared by mixing therewith a lithiumsalt solution or mixture such as, but not limited to LiNO₃, LiOH, LiAc,Li₂SO₄, Li₂Co₃, with a cobalt containing salt solution. In accordancewith one or more embodiments of the invention, the lithium salt cancomprise LiNO₃ and the cobalt salt can comprise Co(NO₃)₂6H₂O. The molarratio of Li/Co can vary but typically ranges from about 0.6 to about1.4. Preferably, the Li/Co molar ratio ranges from about 0.95 to about1.05 so that the molar ratio of the Co content, in the coating layer, tothe Ni content, in the core layer, ranges from about 0.01 to about 0.4,more preferably from about 0.05 to about 0.15.

If any water, which is typically carried with the salts, is present, itis preferably allowed to evaporate utilizing any suitable techniques.For example, the mixture can be heated on a hot plate with stirringuntil dry, or in a rotating drying oven.

The precursor-coated material can then be heated or sintered in airusing any suitable apparatus, such as a muffle furnace to facilitateoxidation and/or crystallization of the coating layer on the core. Forexample, the coating layer can be synthesized by raising the temperatureof the precursor coated Li_(x)Mg_(y)NiO₂ particles at any suitable rate,such as about 5° C. per minute, and maintained or soaked at atemperature of about 450° C. for about one hour. A second soakingtemperature can be utilized by raising the temperature at a rate ofabout 2° C. per minute and maintained at a temperature of about 700° C.for about two hours to promote crystallization of the coating layer.Such an exemplary sintering treatment can provide a coated materialhaving a concentration gradient structure wherein more cobalt can bepresent at or near the outer surface compared to the region at or nearthe core layer. Other techniques may be utilized that provides a coatedcore material having the composition of the present invention.

The drying stage can be performed until the mixture is sufficiently dry.For example, drying can be performed by heating at a rate of about 2° C.per minute to a temperature of about 110° C. The drying temperature canbe maintained as long as necessary and may last from 0 minutes to one ormore hours.

The first heating rate to produce the one or more coating layers canvary and may range from about 2° C. per minute to about 10° C. perminute. The first heat soaking temperature can range from about 300° C.to about 500° C. This first heat soaking temperature can be maintaineduntil the sufficient or desired oxide conversion has been achieved. Itcan be maintained from 0 minutes to one or more hours. The secondheating rate can vary from about 2° C. per minute to about 10° C. perminute. The second heat soaking temperature can range from about 650° C.to about 750° C. It is believed that higher soaking temperatures maypromote degradation of the core layer to other than the preferredcrystallographic arrangement. The coated particles can be allowed tocool to room temperature.

Any suitable equipment may be utilized in the drying/heating/soakingprocess including, for example, any oven or furnace that provides anappropriate oxidizing atmosphere.

The sintered, coated material can be further processed to obtain aparticle sized between about 8 μm to about 12 μm. For example, thesintered, coated material can be ground for about five minutes in amortar grinder fitted with an agate mortar and pestle.

EXAMPLES

The function and advantages of these and other embodiments of thepresent invention can be more fully understood from the examples below.The following examples illustrate the benefits and/or advantages of thecompositions and techniques of the present invention but do notexemplify the full scope of the invention.

In the examples, the following test protocols were performed.

Protocol 1. Rate Capability Test and Formation—1st Cycle Efficiency

A coin cell was used for material life test utilizing lithium metal asthe counter electrode. The positive electrode of the coin cell was madefrom a composite cathode prepared in accordance with Example 2. Theelectrolyte was EC/DEC (1:1)-LiPF₆, 1 M (available from EM Industries,Inc., Hawthorne, N.Y.) and the separator was a glass fiber material(available from Fisher Scientific).

The cell was fully charged and discharged at a rate of C/20 for firstcycle efficiency measurements, which is the ratio of the dischargecapacity vs. the charge capacity. Thereafter the cell was cycled atrates of about C/5, C/2, 1 C, 2 C, 3 C, and 5 C from about 2.7 volts toabout 4.2 volts. 1 C rate was defined as about 150 mAh/g discharge in 1hour.

Protocol 2. Life Cycle Test.

A coin cell was used for material life test. The positive electrode ofthe coin cell was made from a composite cathode, and the negativeelectrode was made from a composite anode, consisting of graphite asmesophase carbon microbeads (MCMB 2528, 90 wt %), PVDF binder (7 wt %)and carbon black (3 wt %). The electrolyte was EC/DEC (1:1)-LiPF₆, 1 M(available from EM Industries, Inc., Hawthorne, N.Y.) and the separatorwas a glass fiber material (available from Fisher Scientific).

The cell was initially fully charged and discharged for 3 cycles atabout C/5 rate, deep cycle. The deep cycles consisted of charging toabout 4.2 V (fully charged) and discharging to about 2.7 V (fullydischarged). The cell was fully charged, to about 4.2 V (100%state-of-charge (SOC)); the cell was then discharged to about 20% offull capacity at about 1 C rate current to reach about an 80% SOC. Thenthe cell was cycled: discharging about 10% (to about 70% SOC) andcharged 10% (to about 80% SOC) at about 1 C rate current, typicallyreferred to as a shallow cycle.

A deep cycle was performed after every 200 shallow cycles. This testprovided an indication of the effective life of the cell underevaluation.

Protocol 3. Area Specific Impedance (ASI) Measurement.

The ASI, in Ωcm², at various starting SOC conditions was determined bypulse discharging a coin cell. ASI was calculated according to:

ASI=A·(ΔV/I),

where A is the electrode area in cm², where I is the discharge currentpulse at a rate of about 6 C. The voltage variation (ΔV) is the voltagechange during the discharge pulse.

For example, at a SOC=90%, the initial voltage is measured. The cell isdischarged at a rate of 6 C and the final voltage is measured after 18sec.

ASI can correlate to the potential available power and allows for acomparison of power capability between materials and formulations forLi-ion cells. This can be particularly important for high pulse powerapplications.

Example 1 Synthesis of Li_(1.05)Mg_(0.025)NiO₂ Composition

A Li_(1.05)Mg_(0.025)NiO₂ composition was prepared and evaluated. Thecomposition was prepared by dry mixing:

about 242.91 g Li(OH)₂ (anhydrous fine powder available fromSigma-Aldrich, Inc., St. Louis, Mo.)

about 14.79 g Mg(OH)₂ (fine powder available from Alfa Aesar, Ward Hill,Mass.)

about 34.97 g LiNO₃ (crystals available from Alfa Aesar, Ward Hill,Mass.)

The mixed materials were added to about 940.31 g Ni(OH)₂ (#543 highdensity spherical powder available from OM Group, Inc., Cleveland, Ohio)in a 1 liter jar. The compounds were mixed by shaking in the jar.

The homogeneous precursor powders (precursor compounds) were placed inalumina crucibles and sintered.

Sintering was performed by heating at a rate of about 5° C./minute toabout 450° C. and held at about 450° C. for about four hours. Thetemperature was then raised at about 2° C./minute to about 700° C. andheld for about four hours.

The sample was then allowed to cool naturally to room temperature. Thecooled sample was ground for about five minutes to break up anyagglomerates. The powder material was sieved through a No. 270 mesh toremove larger particles and to ensure a desired 10 μm particle size.

FIG. 1 is a copy of scanning electron micrograph showing the morphologyof the about 10 μm spherical core material. An X-ray diffraction pattern(XRD) analysis was performed and showed that the produced compositionwas phase-pure with no visible impurities. FIG. 2 is a copy of the XRDplot of the resultant composition. The XRD data shows that the resultingpowder is essentially free of impurities.

Example 2 Fabrication and Electrochemical Performance Evaluation ofLi_(1.05)Mg_(0.025)NiO₂-Based Electrochemical Cells

A Li_(1.05)Mg_(0.025)NiO₂ cathode was fabricated by mixing about 90 wt %active cathode material powder produced as described in Example 1, about6 wt % carbon black (AB100% available from Chevron Phillips ChemicalCompany LP, The Woodlands, Tex.), and about 4 wt % K1120 bindercontaining 12% PVDF in NMP (available from Kureha Chemical of Japan).Additional NMP (n-methylpyrrolidone) was added to produce a desiredviscosity and promote mixing.

The solution was mixed in a 250 ml jar with about 50 steel balls on apaint shaker for about 30 minutes. The mixed slurry was coated onto analuminum foil, about 20 μm thick, with a doctor blade having about a 100μm micron coating gap.

The coated foil was dried at about 130° C. for about thirty minutes. Thedried, coated foil was then densified by passing the dried, coated foilthrough pressurized calendar rolls, about 3 inch diameter, set at about100 psi. The densified, dried, coated foil was cut into about 2 cm²disks for use as electrodes. The active material weight on the diskelectrodes was typically about 20 mg. The disk electrode was dried atabout 80° C. under vacuum for about sixteen hours before cell assembly.

A coin cell (Hosen type #2025) was assembled by utilizing the diskelectrode as the cathode. The coin cell was comprised of a glass fiberseparator containing EC/DEC (1:1)-LiPF₆, 1 M electrolyte (available fromEM Industries, Inc., Hawthorne, N.Y.) and a lithium metal anode. Allassembly operations were performed in an argon-filled glove box whereinwater and oxygen levels were less than about 2 ppm.

The assembled coin cell was evaluated using a cycler/tester (availablefrom Maccor, Inc., Tulsa, Okla.) for capacity, efficiency, ratecapability, power and cyclability, according to protocols 1, 2, and 3,described above. The electrochemical performance of theLi_(1.05)Mg_(0.025)NiO₂ composition (i.e., 0% coating) data are listedin Table 1 below. The discharge voltage profiles at different dischargerates are shown in FIG. 3, which shows that the capacity of theLi_(1.05)Mg_(0.025)NiO₂ composition was typically about 190 mAh/g.

TABLE 1 Electrochemical performance of Li_(1.05)Mg_(0.025)NiO₂-basedcell. LiMg_(y)NiO₂ Core with LiCoO₂ Specific Capacity at Specified RateCoating 1^(st) Cycle Level Efficiency C/5 1C 2C 3C 5C mol % % mAh/gmAh/g mAh/g mAh/g mAh/g  0% 87 203 192 185 180 172  5% 92 202 194 186181 165 10% 89 197 190 179 175 162 15% 90 191 184 173 169 141

Example 3 Safety Testing of Li_(1.05)Mg_(0.025)NiO₂ Cathode

Coated cathodes were prepared and evaluated. The densified electrodeprepared as described in Example 2 was cut into flag-shaped electrodesof about 60×50 mm². The active material weight on the electrode wastypically about 300 mg. Similar to the cathode, an anode was preparedwith formulation of MCMB:PVDF (93:7) was coated on a copper foil and cutto form 60×50 mm² flag electrodes. These were similarly densified bycalendering at 175 psi. The flag electrodes were dried at about 80° C.,under vacuum for about sixteen hours.

A two-electrode bag cell was assembled. The cell was comprised of thedried anode and cathodes, separated by a glass fiber separator with arectangular size of about 65×55 mm². About 1.6 ml of EC/DEC (1:1)-LiPF₆,1 M electrolyte was allowed to soak into the electrodes and separatorand the assembly was compressed between two 70×60 mm² glass plates. Thewhole assembly was put into an aluminum-laminated bag, approximately80×70 mm², and sealed under vacuum.

All assembly operations were performed in an argon-filled glove boxwherein water and oxygen levels were less than about 2 ppm.

The bag cells were charged and discharged at about C/10 current rate,between about 4.1 V to about 2.7 V, then charged at about C/5 currentrate to a capacity of about 180 mAh/g to about 200 mAh/g.

The cells with charged composite cathode were disassembled in anargon-filled glove box. The composite cathode powder was removed fromthe aluminum current collector. The composite electrode powder, withEC/DEC (1:1)-LiPF₆, 1 M electrolyte in a weight ratio ofpowder/electrolyte of 1:1, was loaded into a sealed pressure tight DSCpan. DSC measurements were performed with a continuous scan rate ofabout 5° C./minute up to about 450° C.

The safety data shown in FIG. 13 shows DSC curves ofLi_(1.05)Mg_(0.025)NiO₂ and 5% LiCoO₂ coated material compared toLiNi_(0.8)Co_(0.15)Al_(0.05)O₂ (CA1505N cell available from TODA Co.,Japan). The DSC curves provide a signature of chemical reactivity duringexothermic reactions.

Example 4 Comparison to Li_(1.05)NiO₂-Based Electrochemical Cells

A Li_(1.05)NiO₂ composition was prepared by dry mixing:

about 244.42 g Li(OH)₂ (anhydrous fine powder)

about 35.18 g LiNO₃ (crystals)

The mixed materials were added to about 946.15 g Ni(OH)₂ (OM Group, Inc.#543 High density spherical powder) in a 1 liter jar. The precursorpowder mixture was mixed by shaking.

The precursor powders were placed in alumina crucibles and sintered.Sintering was performed by heating at a rate of about 5° C./minute toabout 450° C. and held at about 450° C. for about four hours. Thetemperature was raised at about 2° C./minute to about 700° C. and heldfor about four hours.

The sample was then allowed to cool naturally to room temperature.

The cooled sample was ground for about five minutes to break up anyagglomerates. The powder material was sieved through a No. 270 mesh toremove large particles and to ensure the desired 10 μm particle size.When subjected to XRD analysis, this material was shown to be phase-purewith no visible impurities. Electrochemical measurements of this powderwere performed in accordance with the procedure described in Example 2.The performance results are listed in Table 2 (i.e., 0% coating).

TABLE 2 Electrochemical performance of LiNiC₂-based cell. LiNiO₂ Corewith LiCoO₂ Specific Capacity at Specified Rate Coating 1^(st) CycleLevel Efficiency C/5 1C 2C 3C 5C atom % % mAh/g mAh/g mAh/g mAh/g mAh/g 0% 89 211 192 184 178 154  5% 88 214 203 197 190 166 10% 90 209 196 192184 168 15% 89 197 185 179 172 151

The data show that the performance, as quantified by specific capacity,of the LiMg_(y)NiO₂-based electrochemical cells of the present invention(see Table 1) are amongst the highest when comparing to the performanceof typical lithium-nickel oxide materials.

Example 5 Comparison to LiCoO₂-Based Electrochemical Cells

A comparable composite cathode in an electrochemical cell was preparedusing LiCoO₂ (C-5 grade available from Nippon Chemical Industrial Co.,LTD., Tokyo, Japan) as the active material. Similar coin cells wereprepared as in the previous example for evaluation.

The electrochemical data of this material are listed in Table 3.

TABLE 3 Electrochemical performance of LiCoC₂-based cell. 1^(st) CycleSpecific Capacity at Specified Rate Efficiency C/5 1C 2C 3C 5C Sample %mAh/g mAh/g mAh/g mAh/g mAh/g LiCoO₂ 97 157 143 127 108 71

The data show that the electrochemical performance of theLi_(1.05)Mg_(0.025)NiO₂-based electrochemical cell of the presentinvention (see Table 1) exceeds the performance of typicallithium-cobalt oxide-based cells, which is the dominating material inthe market presently.

Example 6 Performance of Varying Dopant Levels in Li_(1.05)Mg_(y)NiO₂Material (y=0.005, 0.01, 0.02, 0.025, 0.03, 0.04, and 0.05)

Seven Li_(1.05)Mg_(y)NiO₂ compositions were prepared and evaluated wherey varied from 0.005, 0.01, 0.02, 0.03, 0.04 and to 0.05. The synthesisprocedure for these compositions were substantially similar to theprocedure described in Example 1 except that the levels of Mg(OH)₂ werevaried accordingly to obtain the various dopant levels.

When subjected to XRD analyses, all samples except for the sample havingy=5% were shown to be phase-pure with no visible impurities. For thislatter composition, Li_(1.05)Mg_(0.05)NiO₂, impurities were detectedthat indicated the presence of mixed magnesium oxides.

All samples were then tested electrochemically in coin cells preparedsimilar to the procedure described in Example 2. The results are listedin Table 4.

TABLE 4 Electrochemical Properties of LiMg_(y)NiO₂ at varying Mg dopinglevels. Specific Capacity at Specified Rate Mg Doping 1^(st) Cycle Levelin Efficiency C/20 C/5 1C 2C 3C 5C LiMg_(y)NiO₂ % mAh/g mAh/g mAh/gmAh/g mAh/g mAh/g 0 89 227 211 192 184 178 154 0.005 90 226 210 191 183176 166 0.01 90 223 207 191 184 178 169 0.02 89 218 204 189 183 178 1690.025 87 214 203 192 185 180 172 0.03 87 210 199 187 181 176 167

The data in Table 4 show that the electrochemical performance, e.g., atspecific capacity at 1 C rate, of the LiMg_(y)NiO₂-based cells of thepresent invention was better when compared to the performance ofLiNiO₂-based cells, and superior to the performance of LiCoO₂-basedcells.

Example 7 Synthesis of Li_(1.05)Mg_(0.025)NiO₂ Core Particles Coatedwith a LiCoO₂ Layer

In this example, a lithium-magnesium-nickel oxide composition,substantially prepared as described in Example 1, was coated with alithium-cobalt oxide layer.

To synthesize the coating layer, about 105.55 g LiNO₃ (crystallinepowder, available from Alfa Aesar, Ward Hill, Mass.) and about 445.50 gCo(NO₃)₂.6H₂O (crystalline aggregates, also available from Alfa Aesar)were dissolved in about 200-300 ml distilled water. To which, about 1000g of the Li_(1.05)Mg_(0.025)NiO₂ powder substantially prepared asdescribed in Example 1 was added.

The excess water was removed by evaporation on a hot plate with stirringuntil the mixture became a thick slurry. The slurry was poured into analumina crucible and sintered under the following heating profile: heatat a rate of about 2° C./min to about 110° C., hold for about one hourat about 110° C., heat at a rate of 5° C./min to about 450° C., heatsoak for about one hour at about 450° C., heat at a rate of about 2°C./min to about 700° C., and heat soak for about two hours at about 700°C.

The prepared sample was allowed to cool naturally to room temperature.Once cooled, it was ground for about five minutes to break up anyagglomerates and sieved through a No. 270 mesh screen.

XRD analysis shows that the prepared coated composition had a gradientprofile, with no visible impurities, as can be seen in the copy of theXRD plot presented in FIG. 5 represented here by 5 mol % LiCoO₂ coatedLiMg_(0.025)NiO₂. A copy of an SEM photomicrograph for the same sample,FIG. 4, shows that the coated powder composition maintained itsspherical, about 10 μm, morphology.

Table 1 lists rate capability and first cycle efficiency ofLi_(1.05)Mg_(0.025)NiO₂ core materials coated with various levels ofLiCoO₂ coating. FIGS. 6-8 are graphs showing the discharge profile ofthe LiCoO₂-coated Li_(1.05)Mg_(0.025)NiO₂-based core composition having,respectively, about 5 mol % coating, about 10 mol % coating, and about15 mol % coating. The profiles show that the lithium-magnesium-nickelcomposition can be coated with up to about 15 mol % lithium-cobalt oxidelayer and retain about the same electrochemical performance. FIG. 11 isan XRD comparison of these samples showing increasing gradients withamount of LiCoO₂ coating.

Example 8 Evaluation of LiCoO₂-Coated Li_(1.05)Mg_(0.025)NiO₂ CoreMaterial

Two gradient coated Li_(1.05)Mg_(0.025)NiO₂ materials were synthesizedand coated with about 10% and about 15% LiCoO₂ using the method inExamples 1 and 7. The gradient coating was detected by studying theincreasing degree of asymmetry in the Bragg reflections. In particular,the peak 104 at about 44.4 degrees in 2-theta was used (FIG. 11) to showhow the asymmetry of peak 104 continuously increased with the amount ofLiCoO₂. The respective XRD patterns in FIG. 11 have been adjusted for2-theta zero point position and normalized in intensity for comparison(shown in the insert in the right side of FIG. 11). The gradient coatedsamples were also evaluated electrochemically for rate capability andfirst cycle efficiency as listed in Table 1, according to protocol 1.

Example 9 Comparison of LiCoO₂-Coated Li_(1.05)NiO₂ Core Material

Three gradient coated Li_(1.05)NiO₂ materials were synthesized andcoated with 5%, 10% and 15% LiCoO₂ using the methods as substantiallydescribed in Examples 4 and 7. The coated samples were testedelectrochemically for rate capability and first cycle efficiency asdescribed above and protocol 1. The specific capacity results, listed inTable 2, show that lithium cobalt oxide coated lithium nickel oxidecompounds of the present invention can provide better or at least equalperformance capacity compared to non-coated compounds.

FIG. 9 shows the ASI of a cell utilizing the LiCoO₂-coated Li_(1.05)NiO₂material, measured according to protocol 3 above and FIG. 10 showsseveral ASI measurements of a cell utilizing uncoated LiMgNiO₂ material.As shown in FIGS. 9 and 10, the performance, in terms of potentialavailable power, of the lithium-cobalt-oxide coated lithium-nickel-oxidecells is comparable, if not better than cells utilizing the uncoatedlithium-nickel-oxide materials. FIG. 12 shows the capacity retention ata discharge rate of about 1 C of cells utilizing various activematerials including lithium-nickel oxide, lithium magnesium nickeloxide, lithium-cobalt-oxide coated lithium magnesium nickel oxide,LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ (CA1505 cell available from TODA Co.,Japan), and LiCoO₂ (C-5 grade available from Nippon Chemical IndustrialCo., LTD., Tokyo, Japan). The results presented in FIG. 12 indicate thatthe cells utilizing the coated and uncoated lithium-magnesium-nickeloxides of the invention can have better performance compared to cellsutilizing lithium cobalt oxide. FIG. 13 is a graph showing thedifferential scanning calorimetry of the uncoated and lithium-cobaltoxide-coated lithium-magnesium-nickel oxide material of the presentinvention compared to a commercially available lithium-nickel-cobaltoxide material at about a 100% state of charge and shows that the coatedand uncoated materials are more thermally stable.

Those skilled in the art should appreciate that the parameters andconfigurations described herein are exemplary and that actual parametersand/or configurations will depend upon the specific application in whichthe systems and methods of the present invention are use. Those skilledin the art should recognize or be able to ascertain, using no more thanroutine experimentation, equivalents to the specific embodiments of theinvention. For example, the shape of the particles of the presentinvention, in either the coated or uncoated embodiments, can includeparticles shaped to facilitate packing and/or increase packing and/ortap density such as, but not limited to, plates or having one dimensionsubstantially greater than a second and/or third dimension. Further, arange or combination of particle sizes can also be utilized. Forexample, a mixture of lithium cobalt oxide coated lithium magnesiumnickel oxide particles with uncoated lithium magnesium nickel oxideparticles can be utilized in the systems, device, and techniques of thepresent invention wherein the mixture can have a first type or kind ofparticle, e.g. uncoated, having a first particle size and a second typeor kind of particle, e.g. coated and/or a different Mg loading, having asecond particle size. It is therefore to be understood that theforegoing embodiments are presented by way of example only and that,within the scope of the appended claims and equivalents thereto, theinvention may be practiced otherwise than as specifically described.Further, it is to be appreciated various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Moreover, the present invention is directed to eachfeature, system, or method described herein and any combination of twoor more features, systems, and/or methods, if such features, systems, ormethods are not mutually inconsistent, is considered to be within thescope of the present invention as embodied in the claims. The use of theclarifiers such as “first” and “second” or even “third” and “fourth” isintended to modify an element and does not create an implication ofpriority, precedent, sequence, or temporal order, over another but isintended as labels.

1-23. (canceled)
 24. A method of preparing coated particles comprisingsteps of: providing a first mixture of compounds comprising a lithiumsource, a magnesium source, and a nickel source and heating the firstmixture in an oxidizing atmosphere at a first temperature of about350°-700° C. and for a first period sufficient to crystallize the firstmixture into core particles having a formula Li_(x)Mg_(y)NiO₂ wherein0.9<x<1.3, 0.01<y<0.1, and 0.91<x+y<1.3; and coating the core particleswith a second mixture comprising compounds comprising lithium and cobaltand heating the coated core particles at a second temperature of about600°-800° C. and for a second period sufficient to crystallize amaterial having a formula Li_(a)Co_(b)O₂ wherein 0.7<a<1.3, and0.9<b<1.2.
 25. The method of claim 24 wherein 0.9<x<1.1, 0.02<y<0.05,0.9<a<1.3, and 0.9<b<1.2.
 26. The method of claim 24 wherein heating thefirst mixture comprises heating the first mixture at a rate of about 5°C. per minute to a first soaking temperature of between about 400° C.and 500° C. and heating the first mixture at a rate of about 2° C. perminute to a second soaking temperature of between about 650° C. and 750°C.
 27. The method of claim 26 wherein heating the first mixture furthercomprises maintaining the first soaking temperature for about one toabout six hours and maintaining the second soaking temperature for aboutone to about eight hours.
 28. The method of claim 24 wherein heating thecoated core particles comprises heating the coated core particles at arate of about 2° C. per minute to a third soaking temperature of betweenabout 90° C. and about 120° C.
 29. The method of claim 28 whereinheating the coated core particles further comprises maintaining thethird soaking temperature for about one hour.
 30. The method of claim 29wherein heating the coated core particles further comprises heating thecoated core particles at a rate of about 5° C. per minute to a fourthsoaking temperature in the range from about 300° C. and about 500° C.31. The method of claim 30 wherein heating the coated core particlesfurther comprises maintaining the fourth soaking temperature for aboutone hour.
 32. The method of claim 24 wherein heating the coated coreparticles further comprises heating the coated core particles at a rateof about 2° C. per minute to a fifth soaking temperature in the range offrom about 650° C. to about 750° C.
 33. The method of claim 32 whereinheating the coated core particles further comprises maintaining thefifth soaking temperature for about two hours.
 34. The method of claim24 wherein the magnesium source comprises Mg(OH)₂, the lithium sourcecomprises LiNO₃ and LiOH, and the nickel source comprises Ni(OH)₂.35-38. (canceled)